Provide public type representing parsed hash

[evdokimovs]

Synopsis

In some cases library user may want to parse hash (for validation purposes e.g.) and use it in the future for validating passwords.

Solution

rust-argon2 crate already has Decoded structure which represents parsed hash and decode_string function which parses hash.

I propose to make Decoded structure public, move decode_string function implementation to the FromStr trait and add functions which can verify passwords by Decoded structure.

Also, I propose to rename Decoded structure to the Digest, because for external user Decoded name doesn't make sense. But Digest name also can be confusing. Maybe there is a better name for it?

[mrijkeboer]

Hi @evdokimovs,

Thanks for creating this pull request. I'm not necessarily against providing a public accessible representation of the parsed hash, however, Digest is not the right name for this in my opinion.

[tyranron]

@evdokimovs @mrijkeboer I'd voe for a Decoded name. It's quite straightforward and understandable for me as an external user.